This invention relates to a color image processing apparatus and more particularly to a color image processing apparatus by which excellent color image reproduction can be conducted.
Conventionally, a color image processing apparatus has been used in which a color image is recorded on a recording paper in such a manner that; a color image on a photograph or a text is optically read out by separating it into red R, green G, and blue B; these colors are converted into recording colors such as yellow Y, cyan C, black K, and the like; and the color image is recorded on a recording paper by an image processing apparatus such as an electrophotographic color copier according to the converted colors.
FIG. 4 is a schematic illustration of this type of color image processing apparatus. In FIG. 4, the numeral 1 is a scanner unit which reads out an original image optically and outputs the readout data in the form of digital data of R, G, and B. The numeral 2 is a color reproduction part in which the readout data of R, G, and B is converted into the data of the toner colors of Y, M, C, and K. In the color reproduction part 2, color correction (R, G, B.fwdarw.Y, M, C) and under-color-removal (Y, M, C.fwdarw.Y, M, C, K) are simultaneously conducted according to a lookup-table in order to make 6-bit data of Y, M, C, and K. The numeral 3 is a color balance adjustment part in which the density of colors represented by Y, M, C, and K is adjusted in order to adjust color balance. The numeral 4 is a printer unit by which an image is formed according to the adjusted color data of Y, C, and K. The toner images formed according to the density data of Y, M, C, and K are superimposed on the surface of the photoreceptor drum and finally transferred onto a transfer paper to form a color image.
When a color image is reproduced by the above-described process, a large memory capacity is needed for the color reproduction part 2.
For example, the 6-bit data of R, G, and B is converted into the 6-bit data of Y, M, C, and K by the color reproduction part 2. FIG. 5 is a schematic illustration which shows the composition of the color reproduction part 2. In FIG. 5, the numeral 2a is an even number channel color reproduction table in which the 6-bit data of even numbers (the even number channel) of R, G, and B is converted into the 6-bit density data of Y, M, C, and K. The numeral 2b is an odd number channel color reproduction table in which the 6-bit data of odd numbers (the odd number channel) of R, G, and K. The two tables are substantially the same. The numeral 2c is a channel composition circuit in which the output of the even number channel color reproduction table 2a and that of the odd number channel color reproduction table 2b are composed. The even number channel color reproduction table and the odd number channel reproduction table are composed of ROM into which the 6-bit data of R, G, and B is inputted as the address input and from which the 6-bit data of Y, M, C, and K stored in the memory is outputted. The reason why the channel is divided into the even number channel and the odd number channel is to process the data at a high rate of speed taking the access time into consideration. To go into more details, color reproduction processing is conducted by both the odd number channel color reproduction table and the even number channel color reproduction table in such a manner that; the first pixel data of R, G, and B input data is processed in the odd number channel color reproduction table 2b; the second pixel data is processed in the even number channel color reproduction table 2a; the third pixel data is processed in the odd number channel color reproduction table 2b; and so on. After the color data is processed in the two tables, the processed data is composed in the channel composition circuit 2c. According ly, even if the memory access time is a little longer, it causes no problem. Since image formation at the printer unit 4 is conducted four times in order of Y, M, C, and K, color reproduction is also conducted four times in accordance with image formation.
As color data processing is conducted in the manner described above, too much memory capacity is required of the color reproduction table of ROM composition, which will be explained as follows. Because each of R, G, and B needs a memory capacity of 6 bits to be stored, the memory capacity needed for the color reproduction table is address 18 (6.times.3) bits. When each of Y, M, C, and K data is stored in 1 byte, the necessary capacity of the memory amounts to 2.sup.18 .times.4=1 M bits (each pixel channel).
The disadvantage of this color image processing apparatus is that excessive memory capacity is required. Since the same processing is conducted in each pixel channel, the advantage of dividing the color data into pixel channels is little.